An organic EL (electroluminescence) device, a typical example of an organic semiconductor device, is a light emitting element which utilizes a luminous phenomenon during recombination of electrons and holes in an organic semiconductor layer. More specifically, the organic EL device comprises an organic semiconductor light emitting layer, an electron injecting electrode for injecting electrons to the organic semiconductor light emitting layer, and a hole injecting electrode for injecting holes to the organic semiconductor light emitting layer (Patent Reference 1).
The light emission of such organic electroluminescence element is turned on/off by turning on/off a voltage applied between the hole injecting electrode and the electron injecting electrode. Further, emission intensity is modulated by variably controlling the voltage applied between the hole injecting electrode and the electron injecting electrode.    Patent Reference 1: Japanese Unexamined Patent Publication No. 05-315078 (1993)